1. Field of the Invention
The present invention relates to an information storage apparatus for recording information on a recording medium and reproducing information from the recording medium using a scanning probe, and more particularly, to an information storage apparatus of a recording medium having a ferroelectric film.
2. Description of the Related Art
As the demand for small-sized products such as portable communication terminals and electronic notes increases nowadays, highly integrated micro nonvolatile recording media are increasingly required. It is uneasy to small-size existing hard disks and to highly integrate flash memories. Thus, recording media using a scanning probe have been studied as an alternative plan. Here, the scanning probe represents a probe used in a scanning tunneling microscope (STM), an atomic force microscope (AFM), or a scanning probe microscope (SPM).
The recording media includes recording media which are formed of a ferroelectric substance, a ferromagnetic body, a thermoplastic resin or thermosetting resin. A method of recording information on the recording media includes a method of using electromagnetic force that reverses a domain of a ferroelectric substance or ferromagnetic body of a recording medium with a scanning probe and a method of inducing phase shift by applying heat to a recording medium or physically forming a mark on the recording medium to recode information.
Also, a method of reproducing information recorded on the recording media includes a method of sensing electrostatic force, electrostatic magnetic force, piezoelectric force, and the like operating at a probe and a method of sensing variations in characteristics of a recording medium such as the difference in an electric conductivity or a heat conductivity.
For example, FIG. 1 is a view of an ultradensity information storage apparatus using a ferroelectric thin film disclosed in Korea Patent Publication No. 2001-19871. Referring to FIG. 1A, the ultradensity information storage apparatus includes a recording medium 110, a head 120, and a control unit 130. The recording medium 110 stores information. The head 120 reads information recorded on the recording medium 110. The control unit 130 analyzes polarity of a dielectric polarization using an electric signal and controls the head 120 which is related to the polarity of the dielectric polarization. The head 120 includes a probe unit 25 and a scanner 22, and the control unit 130 includes a controller 32, a computer 33, and a lock-in amplifier 31.
Referring to FIG. 1B, the recording medium 110 includes a substrate 41, an electrode layer 42 that is stacked on the substrate 41, and a ferroelectric film 43 that is stacked on the electrode layer 42. Referring to FIG. 1C, the probe unit 25 includes a probe 40a, a cantilever 40b for supporting the probe 40a, and a piezoelectric substance 45 between the probe 40a and the cantilever 40b. 
The ultradensity information storage apparatus applies an alternating current (AC) having a predetermined frequency to the probe 40a in a state that the ferroelectric film 43 contacts the probe 40a, amplifies variations in amplitude of the ferroelectric film 43 based on the AC due to electric force between dielectric polarizations using the lock-in amplifier 31, analyzes the variations, and detects information on the dielectric polarizations.
A method of reproducing information in a state that a probe contacts a recording medium has a problem of wearing the probe and the recording medium.
A method of sensing force to reproduce information has a disadvantage in that resonance frequency (generally, 1 MHz or less) of a cantilever limits a speed for reproducing information. In particular, since a method of sensing a polarized state of a domain of a ferroelectric thin film using piezoelectric force has to use a lock-in amplifier for amplifying a signal sensed from a recoding medium, it is difficult to further reduce the size of an ultradensity information storage apparatus.
It is difficult to further reduce the size of an information storage apparatus since the method of reproducing information in a state that the probe contacts the recording medium needs a feedback circuit for every probe to maintain the uniform distance between the probe and the recording medium.